Our present invention relates to a three-point hitch for a tractor and capable of raising and lowering and/or swinging an attachment which can be mounted by the three-point hitch on the front or rear of the tractor.
The three-point hitch of a tractor can be utilized to affix an attachment to the tractor and for raising, lowering or swinging that attachment. The attachment is usually an agricultural appliance or a soil-working or ground-working tool. Typical attachments for a tractor are attachments such as blades or the like for modifying ground contours, agricultural attachments such as fertilizing, harvesting and cultivating attachments including plows, harrows, manure spreaders and the like.
The three-point hitch permits the position of the attachment to be raised or lowered on the tractor and the three-point hitch also serves to enable the working height to be adjusted.
For this purpose the three-point hitch normally has some actuator for the lower links, the upper link being generally passive.
In modern tractors, the hitch may also be associated with a control system for maintaining a position of the attachment with respect to the ground in spite of irregularities in the latter.
It is an object of the present invention to provide a three-point hitch for the purposes described which is especially simple and reliable and can provide an optimum lifting force characteristic, a reduced overall height or size and significantly less weight than earlier three-point hitches.
Another object of the invention is to provide a low cost three-point hitch of high versatility.
These objects are attained, in accordance with the invention in a three-point hitch for a tractor or other vehicle upon which an attachment may be mounted which is capable of raising or lowering or swinging the attachment and which can be mounted on the front and/or the rear of the tractor. According to the invention, a hitch bracket is provided for mounting on the tractor and the lower links are swingable on the hitch bracket or relative to the hitch bracket at the tractor side at lower pivots while the upper link is swingable on the hitch bracket at the tractor side at an upper pivot.
The lower links have, at their attachment side or ends lower coupling points while the upper link has at the attachment side an upper coupling point for connection to the attachment at points which lie at the vertices of a triangle. The lower links and/or the upper link can be provided with piston-and-cylinder units for raising, lowering and/or swinging them. When reference is made to pivots at the tractor side, of course, those pivots need not be provided directly on the tractor but need only be provided on the side of the links toward the tractor, e.g. on the hitch bracket, on the tractor itself or a structure intervening between the links and the tractor. The three-point hitch of the present invention is suitable for attachment to the front and/or rear on a tractor and can be a unit premounted with all of its components and preadjusted so that it can be attached to the tractor as a unit or can be affixed to a tractor which does not have such a hitch. The hitch, therefore, can be used to retrofit a tractor or other vehicle with the system for raising, lowering and swinging the coupling points for attachment.
The hitch bracket itself may be equipped with a raisable and lowerable connection to the tractor and can be selectively used as a pickup hitch or an adjustable draw bar or the like. The invention, in addition, provides a three-point suspension for an attachment with a kinematic relationship corresponding to a linear or slightly progressive lifting force characteristic. It is useful for large and small loads and can provide both a longitudinal and lateral inclination adjustment. The invention also provides that stabilizers can be connected to the lower links. The stabilizers can be, for example, piston-and-cylinder units which are pivotally connected on the one hand to the tractor and on the other hand to the lower links. In a preferred embodiment, however, the stabilizers can be piston-and-cylinder units which are integrated in the lower links and are oriented substantially perpendicular to the longitudinal axis of the tractor and can have piston rods carrying stabilizer jaws which engage cams provided on the hitch bracket and extending in the direction of the tractor longitudinal axis. The lateral forces can thus be taken up by these piston-and-cylinder units.
According to a feature of the invention, lever or other force-transmission ratio devices can be provided to control the sway or effect the raising and lowering movement. With such devices, relatively small piston-and-cylinder units can be used with comparatively short strokes.
The invention enables the system to be free from the customary connections to the rear axle of the tractor. After lifting of the attachment from the ground or out of the ground, the electronic circuitry which may be coupled to the stabilizers and other piston-and-cylinder units and which can be responsive to detection of the stroke thereof can automatically switch the stabilizers into a xe2x80x9crigidxe2x80x9d status.
The stroke can be measured by a potentiometer or limit switch. The three-point hitch of the invention can fulfill all of the requirements established by the German Industrial Standards (DIN) and the VDI standards for upper links, lower links, lifting rods and three-point hitches for rear mounting on a tractor, including the safety requirements.
The lower links can be formed from two plug-in link parts whereby the front link parts can have receptacles for the stabilizers or can be premounted with the stabilizers.
Both sides of the hitch bracket can be equipped with mounts, especially mounting cheeks for the cylinder unit acting upon the lower links. The mounts have U-shaped cross sections and can partly or fully receive the cylinder units. The cylinder units can be pivotally connected, via appropriate bearings, with the mount while the lower end of the cylinder unit can be coupled with the lower link by a respective fork and, if desired, with bearings at the pivots. The result is a so-called xe2x80x9cdrawing cylinderxe2x80x9d.
In another embodiment, the piston unit is connected pivotally via an appropriate bearing arrangement with the mount while at the upper end, the cylinder unit works via a lever to actuate the rod. Bearings are provided here too between the pivot connection of the cylinder unit with the lever and the lever with the mount. A further bearing arrangement can be provided between the rod and the lever. In this case the cylinder unit is a lifting cylinder.
Of course, the upper link can be formed as a piston-and-cylinder unit as well and the latter can act on the triangular construction interconnecting the coupling points. The hitch described is simple and reliable and is of comparatively small size and weight so that it can be fabricated at lower cost than heretofore. The compact construction is a function in part of the rearward shift of the pivot points for the lower links as well as the shift in positions of the cylinder units. The arrangement and configuration of the stabilizers also contributes to a reduction in the size and weight of the three-point hitch.
The three-point hitch of the invention does not require mounting of a variety of components on the transmission casing of the tractor and there is more room at the back or front of the tractor, utilizing the system of the invention. The fact that the stabilizers act inwardly ensures a greater amount of space for the tractor cylinders. The stabilizers have been found to be highly advantageous for small tractors, i.e. tractors suitable for horticulture and viniculture. The cabling of the system can be independent of the mounting of the three-point hitch on the tractor and that, of course, can contribute to a saving in mounting costs. Another cost conserving feature is the elimination of any need to modify the transmission to accommodate parts of the three-point hitch. The three-point hitch of the invention also reduces the forces which are applied via the hitch bracket to the tractor.